Engine performance and efficiency engine may be improved by combining a central throttle with port throttles. The central throttle regulates air flow into a plurality of cylinders while each port throttle regulates air flow into a single cylinder. In one example, a central throttle may be positioned in an engine air intake system upstream of an engine air intake manifold that routes air from the central throttle to engine cylinders. Intake manifold runners direct air from the intake manifold to intake ports. A port throttle positioned within each intake port leading to a cylinder, or alternatively within each intake manifold runner, regulates air flow into an individual engine cylinder. However, it may be difficult to cooperatively control port throttles with a central throttle. For example, during higher load conditions, it may be desirable to fully open port throttles to improve cylinder air flow. At lower engine loads, it may be desirable to control air flow into engine cylinders at least in part via the port throttles. Therefore, it may be difficult to provide a desired cylinder air amount when transitioning between conditions where port throttle position affects cylinder air amount and conditions where port throttle position has little or no effect on cylinder air amount.
The inventors herein have recognized the above-mentioned limitations and have developed an engine operating method, comprising: providing a transition from a first throttle control mode to a second throttle control mode in response to a change in engine operating conditions; and adjusting intake manifold pressure via a first throttle responsive to a desired cylinder air charge in the first throttle control mode and adjusting intake port pressure via a second throttle responsive to the desired cylinder air charge in the second throttle control mode.
By adjusting intake manifold pressure and/or intake port pressure depending on operating conditions during transitions between throttle control modes, it may be possible to provide a desired cylinder air charge. For example, if a driver requests a change from a higher brake mean effective pressure (BMEP) to a lower BMEP, the throttle control mode may be changed to improve engine efficiency and/or performance. Cylinder air charge may be adjusted and quickly converged to a desired cylinder air charge by changing intake port pressure via a port throttle. The intake manifold pressure may be allowed to evolve at a different rate by closing the central throttle differently than the port throttle. In other examples, the port throttle may be maintained in a substantially fully open position (e.g., within 10% of full open) while intake manifold pressure is adjusted via a central throttle to provide the desired cylinder air charge. In this way, the desired cylinder air charge may be provided by selectively controlling the intake manifold pressure and/or intake port pressure to provide the desired cylinder air charge.
The present description may provide several advantages. Specifically, the approach may provide improved transient air flow control when switching between throttle control modes. Further, the approach may provide improved cylinder air-fuel control at lower engine loads, thereby improving engine emissions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.